An item of electronic equipment that dissipates more power than can easily be cooled with heat sinks alone generally uses fans to supplement natural convection. This works well enough, but as anyone who has labored in a room full of fan cooled equipment can attest, the noise from the fans themselves can be rather annoying. This is especially so in an office setting, where there arise issues of decorum, in addition to the more pragmatic issues of productivity reduction owing to distractions caused by noise.
A significant amount of fan noise appears to originate with the production of turbulent vortices of air at the tips of the fan blades as they rotate about the fan axis. The tips slice sideways, as it were, through low pressure air on the inlet side of the blades and the high pressure air on the outlet side of the blades. As the blades rotate, high pressure air spills over the tips of the blades and imparts an off-axis spinning motion in the low pressure air creating vortices whose behavior results in the production of acoustic energy (noise), particularly when the blades pass the struts of the fan. In addition, the aerodynamic performance of the fan does not reach its full potential capacity due to parasitic energy losses at the blade tips.
Most commercially available fans do nothing to eliminate the noise resulting from the blade vortices. Instead, noise is managed by decreasing fan speed or blade pitch, both of which compromise the aerodynamic performance of the fan.
Accordingly, it would be desirable if fan noise could be reduced without sacrificing the air flow that fan is intended to supply
The present invention is directed to a system and method which minimize blade tip vortices of a fan and thus reduce a noise source, resulting in a quieter higher performance fan. Small winglets (similar to those observed on aircraft wings) placed at the end of each fan blade substantially eliminate the vortices created in conventional fans by the pressure differential between the top side (low pressure) and the bottom side (high pressure) of the blade. The winglet acts as a barrier between the low pressure and high pressure sides of a blade, which prevents leakage around the tip, thus suppressing vortices. The winglet can be placed at the end of the blade opposite the hub on either top, bottom, or both top and bottom of the blade.
Technical advantages of embodiments of this invention include noise reduction, because there are no shedding vortices to create noise as the blades pass the struts; increased aerodynamic efficiency of the fan, providing higher air flow for the same fan speed, size, and power, because energy is not lost in vortices; and minimal cost impacts, because housings currently used for fans can still be used with standard finger guards and because the blades are typically plastic injection molded.